1. Field of the invention
The present invention relates to a plate brick for a sliding gate nozzle (hereinunder referred to as "SN") apparatus which is used for controlling a flow rate of a molten metal on casting.
2. Description of the Prior Art
An SN apparatus is generally composed of three parts, namely, an upper nozzle, a plate brick consisting of a fixed plate and a sliding plate, and a lower nozzle. Among these, the plate brick is a part which is required to have specialized properties for the function of controlling the flow rate of a molten metal.
Since the plate brick is subject to physical and chemical attack such a violent thermal shock and wear caused by a stream of molten metal, spalling resistance and corrosion resistance are the most important properties required for working the plate brick. Further, in order to obtain stable high durability, oxidation resistance and mechanical strength are also important properties to have in addition to the above properties.
The present inventors previously disclosed in Japanese Patent Publication No. 60-29664 an improved SN plate in resistance against the deterioration of the mechanical strength in the middle temperature range (400.degree. to 700.degree. C. and the spalling resistance and the corrosion resistance which is prepared by admixing 2 to 15 wt % of a thermosetting synthetic resin such as phenol resins, furan resins and epoxy resins with a refractory aggregate including 1 to 20 wt % of a powder of a low-melting metal having a particle size of not more than 0.5 mm, molding and heating the resultant mixture, to a temperature of not higher than 800.degree. C.
Improvement in the mechanical strength of thus prepared SN plate brick was achieved by heating at temperatures from about 150.degree. to 250.degree. C.
There are, however, problems still remaining unsolved. For example improvement of mechanical strength at a temperature higher than 300.degree. C., temperatures which the SN plate is in practical operation subjected to, cannot be expected due to oxidation in prior art SN plates.